Semiconductor device and method of fabricating the same

ABSTRACT

A method of fabricating a semiconductor device having a non-volatile memory cell includes forming an insulation layer as an uppermost/outermost portion of the memory cell to enhance the charge retention capability of the memory cell. The insulation layer is formed after the gate structure and integrate dielectric of the non-volatile memory cell, and a gate of a logic transistor are formed. The insulation layer thus enhances the function of the intergate dielectric. Subsequently, a conductive layer is formed on the substrate including over the gate of the logic transistor. A silicide layer is then formed on the gate of the logic transistor and on the substrate adjacent opposite sides of the gate. The insulation layer thus also serves prevent the formation of a silicide layer on the non-volatile memory cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 11/048,845, filed Feb. 3, 2005, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and to a method of fabricating the same. More specifically, the present invention is directed to a semiconductor device having a non-volatile memory cell and to a method of fabricating the same.

2. Description of the Related Art

Non-volatile memory cells continuously hold their stored data even when their power supplies are interrupted. Typically, a non-volatile memory cell has a gate stack structure. Specifically, a non-volatile memory cell has a gate stack and a source/drain formed at opposite sides of the gate stack. The gate stack includes a gate insulation layer, a floating gate, an intergate dielectric, and a control gate which are sequentially stacked on a substrate. Charges are introduced to the floating gate through a tunnel insulation layer to be stored therein. The stored charges set a threshold voltage of the cell. A non-volatile memory cell stores data using the cell threshold voltage.

The fabricating a non-volatile memory device includes a photolithographic process following the formation of the intergate dielectric. Specifically, the photolithographic process is carried out to form the control gate on the intergate dielectric. In this case, the intergate dielectric may be damaged during the photolithographic process. Also, the intergate dielectric may be additionally damaged during a subsequent process in which a spacer is formed. Damage to the intergate dielectric degrades the reliability of the non-volatile memory device because if charges stored in the floating gate migrate through the damaged intergate dielectric during operation of the cell, the threshold voltage of the cell fluctuates. Hence, the data stored in the cell is altered.

Also, it might be desirable to produce a semiconductor device in which a logic transistor is integrated with the non-volatile memory cell. Conventionally, logic transistors may include a silicide layer to enhance the operating speed thereof. However, a silicide layer can not withstand the high program voltage of a non-volatile memory cell.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a semiconductor device that includes a highly reliable non-volatile memory cell.

Another object of the present invention is to provide a semiconductor device that includes both a non-volatile memory cell and a logic transistor which can operate at a high speed.

According to one aspect of the present invention, a method of fabricating a semiconductor device includes (a) preparing a substrate including a first area where a logic transistor is to be formed and a second area where a non-volatile memory cell is to be formed, and (b) forming a logic transistor and a non-volatile memory cell at the first and second areas, respectively,

wherein the forming of the non-volatile memory cell includes forming an insulation layer as an outermost portion of the non-volatile memory cell to enhance the charge retention capability of the cell, and the forming of the logic transistor includes selectively forming a silicide layer at the first area of the substrate.

The non-volatile memory cell and the logic transistor may be formed by forming a first gate insulation layer and a second gate insulation on the first and second areas of the substrate, respectively, forming a first (floating) gate and an intergate dielectric on the first gate insulation layer, and forming a second gate on the first gate insulation layer and a second (control) gate on the intergate dielectric. The silicide layer is formed on the substrate adjacent opposite sides of the gate formed at the first area of the substrate and on the gate itself at the first area. The insulation layer covers the gate structure and the substrate at the second area to prevent the formation of a silicide layer at the second area and to enhance the function of the intergate dielectric.

The silicide layer may be formed by forming a metal layer over the entire surface of the substrate and performing a silicide heat-treating process. A silicide layer is not formed at the second area, i.e., the area where the non-volatile memory cell is formed, because the insulation layer covers the second area. On the other hand, the gate at the first area, and the silicon exposed adjacent opposite sides of the gate, react with the metal layer to form a silicide layer at the first area, i.e., the area where the logic transistor is formed.

According to another aspect of the present invention, an I/O transistor is formed at a third area of the substrate. In this case, the gate insulation layer is also formed at the third area of the substrate, and a gate of the I/O transistor is formed on the third area of the substrate. Preferably, the gate of the I/O transistor is formed at the time the gate of the logic transistor is formed on the second area of the substrate, and the (control) gate of the non-volatile memory cell is formed on the integrate dielectric at the third area of the substrate. In this case, the insulation layer is formed over the second and third areas of the substrate.

According to yet another aspect of the present invention, the present invention provides a semiconductor device including a first gate formed on a gate insulation at an upper portion of a substrate, an intergate dielectric disposed on the first gate, a second gate overlying only a portion of the intergate dielectric such that another portion of the first gate is left exposed by the second gate, and an insulation layer extending over at least that portion of the intergate dielectric left exposed by the second gate. Accordingly, the insulation layer protects the integrate dielectric and enhances the function thereof.

According to another aspect of the present invention, the insulation layer may include an oxide or silicon oxynitride. Preferably, the enhancing insulation layer is a multi-layered film including both an oxide and a nitride. For example, the enhancing insulation layer may be an oxide-silicon oxynitride-silicon nitride film, a silicon-silicon oxynitride-oxide film, an oxide-silicon nitride-silicon oxynitride-silicon nitride film, or an oxide-silicon nitride-oxide film. The aforementioned materials appear stacked in the films in the order named.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a semiconductor device according to the present invention.

FIG. 2 through FIG. 7 are cross-sectional views of a substrate, corresponding to cross-sectional views taken along lines I-I′, II-II′, and III-III′ in FIG. 1, and illustrating a method of fabricating a semiconductor device according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In the drawings, the thickness of layers and regions are exaggerated for clarity. Also, like numbers refer to like elements throughout the specification. Still further, when a layer is referred to as being “on” or “over” another layer or substrate, such a description may refer to either the layer in question being disposed directly on the other layer or substrate or may refer to intervening layers being present therebetween.

Referring to FIG. 1, a semiconductor device according to the present invention includes a logic transistor 180 a, an input/output transistor (hereinafter referred to as “I/O transistor”) 180 b, and a non-volatile memory cell 180 c. In FIG. 1, characters ‘a’, ‘b’, and ‘c’ denote a logic transistor forming area in which the logic transistor is formed, an input/output transistor forming area (hereinafter referred to as “I/O transistor forming area”) in which the I/O transistor is formed, and a memory cell forming area in which the non-volatile memory cell is formed, respectively.

Also, in FIG. 1, reference numerals 100 a-100 c denote active regions, reference numeral 120 denotes a floating gate of the non-volatile memory cell 180 c, reference numeral 130 denotes an intergate dielectric of the non-volatile memory cell 180 c, reference numeral 150 c denotes a control gate of the non-volatile memory cell 180 c, reference numeral 150 a denotes a gate of the logic transistor 180 a, reference numeral 150 b denotes a gate of the I/O transistor 180 b, and reference numerals 110Sa-110Sc and 110Da-110Dc denote source/drain regions formed at opposite sides (active regions) of the gates 150 a, 150 b and 120. Although not shown in this figure, a gate insulation layer is disposed between the gates 150 a, 150 b, 120 and a substrate.

The logic transistor 180 a also has silicide layers 170S/170D and 170G on the source/drain region 110Sa/100Da and the gate 150 a. The control gate 150 c of the non-volatile memory cell 180 c is smaller than the floating gate 120 so as to provide a high coupling ratio and margin for the photolithographic process used to produce the gates. The control gate 150 c overlies the floating gate 120 outside the active region 100 c. Also, the non-volatile memory cell 180 c includes an insulation layer for enhancing the charge retention of the intergate dielectric 130 (not shown in this figure). The insulation layer is formed at least on an intergate dielectric exposed by the control gate 150 c.

A method of fabricating the semiconductor device shown in FIG. 1 will now be described with reference to FIG. 2 through FIG. 7.

As illustrated in FIG. 2, a substrate 200, which includes a logic transistor forming area ‘a’, an I/O transistor forming area ‘b’, and a non-volatile memory cell forming area ‘c’, is prepared. Next, a conventional device isolation process is carried out to form a device isolation layer 202. Regions surrounded by the device isolation layer 202 become the active regions. Gate insulation layers 204 a-204 c are formed on the substrate 200 in the active regions using conventional techniques. The gate insulation layers 204 a-204 c have thicknesses that are suited to the characteristics required of the device. A floating gate 206 and an intergate dielectric 208 are sequentially formed on the gate insulation layer 204 c at the memory cell forming area ‘c’. Specifically, a gate layer made of, for example, polysilicon, and then a multi-layered film are formed over the entire surface of the substrate. The multi-layered film is an oxide-nitride-oxide (ONO) film. The multi-layered film and gate layer are then patterned using a photolithographic process to form the gate 206 and intergate dielectric 208 at the memory cell forming area ‘c’. Subsequently, an ion implanting process is carried out to form an impurity diffusion region, e.g., source/drain regions, at opposite sides of the floating gate 206.

As illustrated in FIG. 3, a second gate layer 210 is formed over the entire surface of the substrate 200. The second gate layer 210 is made of, for example, polysilicon.

As illustrated in FIG. 4, a photolithographic process is carried out to form a logic gate 212 a, an I/O gate 212 b, and a control gate 212 c at the logic transistor forming area ‘a’, I/O transistor forming area ‘b’, and memory cell forming area ‘c’, respectively. The control gate 212 c is smaller than the floating gate 206. An ion implanting process is carried out to form impurity diffusion regions at opposite sides of the logic gate 212 a in the logic transistor forming area ‘a’, and at opposite sides of the I/O gate 212 b in the I/O transistor forming area ‘b’. The memory cell area ‘c’ is covered with a mask during this process.

Next, a spacer insulation layer is formed over the entire surface of the substrate 200. An etch-back process is then carried out to form spacers 214 a and 214 b on sidewalls of the logic gate 212 a and I/O gate 212 b, and to form spacers 214 c 1 and 214 c 2 on sidewalls of the floating gate 206 and control gate 212 c. The sidewall spacers may be made of, for example, a nitride or oxide. Although an upper oxide layer of the intergate dielectric 208 is etched, the insulation layer mitigates the etching of the oxide, as will be described later.

As illustrated in FIG. 5, an insulation layer 216 is formed on the substrate 200 over the I/O transistor forming area ‘b’ and the memory cell forming area ‘c’. More specifically, an insulation layer is first formed over the entire surface of the substrate 200, and then a photolithographic process is carried out to remove the insulation layer from the logic transistor forming area ‘a’ while leaving the remainder of the insulation layer in the I/O transistor forming area ‘b’ and the memory cell forming area ‘c’.

The insulation layer 216 comprises an oxide or a nitride. Also, the insulation layer 216 may be a multi-layered film comprising, for example, oxide 216 a, oxynitride 216 b, and oxide 216 layers that are stacked in the foregoing order. Alternatively, the insulating layer 216 may be a multi-layered film comprising oxide-silicon nitride-silicon oxynitride-silicon nitride and oxide-silicon nitride-oxide layers that are stacked in the foregoing order. In the case in which the insulation layer 214 is a multi-layered film, its lowest layer preferably comprises an oxide.

As illustrated in FIG. 6, a metal layer 218 is formed over the entire surface of the substrate 200. The metal layer 218 may be of a material which can react with silicon to form a silicide, i.e., a material having a low resistivity. The metal layer 216 may comprise a material having a high fusion point such as cobalt, nickel, or titanium. The metal layer 218 does not contact the substrate 200 or gates at the I/O transistor forming area ‘b’ and the memory cell forming area ‘c’ because the areas ‘b’ and ‘c’ are covered with the insulation layer 216.

As illustrated in FIG. 7, a silicide heat-treating process is carried out to form silicide layers 220S, 220D, and 220G at the logic transistor forming area ‘a’. That is, a silicide layer is selectively formed on an impurity diffusion region and a gate. Subsequently, the non-reacted metal layer is removed from the I/O transistor forming area ‘b’ and the memory cell forming area ‘c’.

According to the present invention as described above, an insulation layer enhances the charge retention capability of the memory cell. Furthermore, a silicide layer is selectively formed at the logic transistor to enhance the operating speed of the logic transistor. Such a silicide layer, though, is not durable to the high program voltage of a non-volatile memory cell. However, according to the present invention, the insulation layer prevents the forming of a silicide layer on the control gate of the memory cell. Therefore, a highly integrated semiconductor device having a reliable memory cell can be fabricated by performing a relatively simple process.

Finally, although the present invention been described above with reference to the preferred embodiments thereof, it is to be understood that the present invention is not limited to those precise embodiments. Rather, various changes and modifications may be made to those embodiments by one of ordinary skill in the art without departing from the true scope or spirit of the invention as defined by the appended claims. 

1. A semiconductor device comprising: a substrate; a gate insulation layer at an upper portion of the substrate; a first gate disposed on the gate insulation layer; an intergate dielectric on the first gate; a second gate disposed on only a portion of the intergate dielectric such that another portion of the intergate dielectric is left exposed by the second gate; and an insulation layer extending over at least the portion of the intergate dielectric left exposed by the second gate.
 2. The semiconductor device as recited in claim 1, wherein the insulation layer is a film selected from the group consisting of an oxide-silicon oxynitride-silicon nitride film, a silicon-silicon oxynitride-oxide, oxide-silicon nitride-silicon oxynitride-silicon nitride film, and an oxide-silicon nitride-oxide film.
 3. The semiconductor device as recited in claim 1, wherein the substrate has an active region, the first gate overlies the active region of the substrate, the second gate has a smaller area than the first gate, and the second gate overlies the first gate over a portion of the substrate outside the active region of the substrate.
 4. The semiconductor device as recited in claim 1, wherein the first gate, the integrate dielectric, the second gate and the insulation layer constitute a non-volatile memory cell of the device, and further comprising: a logic transistor disposed on a first area of the substrate, said logic transistor including a logic gate disposed on the gate insulation layer, and a silicide layer, and wherein said insulation layer terminates outside side the first area of the substrate. 